Since we began doing football research a few years ago, weve developed a number of axioms that tend to come up over and over again, both on our Web site and in Pro Football Prospectus. With both Shaun Alexander and Edgerrin James entering free agency this off-season, one precept in particular got a lot of attention: the 370-carry theory.

The 370-carry theory is generally summarized as follows: A running back with 370 or more carries during the regular season will usually suffer either a major injury or loss of effectiveness the following year, unless he is named Eric Dickerson.

Some recent examples of the 370-carry theory in action include Curtis Martins collapse last year [i.e. 2005], Jamal Lewiss struggles for the last two years, and Ricky Williams falling from 4.8 yards per carry in 2002 to 3.5 yards per carry in 2003. Terrell Davis, Jamal Anderson, and James each tore his ACL a year after going over 370 carries. The 370-carry barrier helped destroy the careers of Earl Campbell, Barry Foster, and Gerald Riggs.

Not counting Alexander, there have been 14 players who did not reach 370 carries in the regular season, but surpassed 390 carries during the postseason. Though some of these players continued to play well the next season and even afterwards, a number of them had major difficulties.

Terrell Davis (1997): 369 carries, 481 including the postseason. The latter total is an NFL record. Davis was spectacular again in 1998, but that season’s total of 392 regular-season carries basically ended his career.

Eddie George (1999): 320 carries, 428 including the postseason. He fell from 4.1 to 3.7 yards per carry in 2000, and after 403 regular-season carries he was never again an effective player.

Curtis Martin (1998): 369 carries, 418 including the postseason. Martin saw no ill effects; 1998 was actually his worst year until 2005.

Thurman Thomas (1993): 355 carries, 418 including the postseason. Thomas continued to play well but never again was able to carry the ball 300 times in a season.

Joe Morris (1986): 341 carries, 414 including the postseason. The following year Morris plummeted from 4.4 to 3.4 yards per carry. By 1989, his career was over due to nerve damage and broken bones in his feet, except for a short-lived comeback with the 1991 Browns.

Jamal Lewis (2000): 309 carries, 412 including the postseason. 103 postseason carries is the third-highest total in history, and Lewis tore his ACL the next year.

Corey Dillon (2005): 345 carries, 410 including the postseason. Fell from 4.7 to 3.5 yards per carry and only managed 12 games due to injuries.

Ahman Green (2003): 355 carries, 403 including the postseason. Dropped from 5.3 yards per carry in 2003 to 4.5 yards per carry in 2004 and then 3.3 yards per carry in 2005, when he missed 11 games because of injuries.

Earl Campbell (1979): 368 carries, 401 including the postseason. Improved in 1980, when another heavy workload cost him most of his effectiveness in 1981 and beyond.

Natrone Means (1994): 343 carries, 400 including the postseason. Only played 10 games the following year due to injuries, never again played a full season, and retired in 2000 at the age of 28.

Dorsey Levens (1997): 329 carries, 400 including the postseason. Only played seven games in 1998, never again had 100 carries in a season after 1999, didn’t average four yards per carry again until 2002.

Curt Warner (1983): 335 carries, 395 including the postseason. Blew out his knee during the first game of 1984 and was out for the season.

Emmitt Smith (1994): 368 carries, 395 including the postseason. Had his best season in 1995, then declined after that.

To summarize, eight of these 14 players were injured or lost effectiveness the following season. A ninth, Thomas, was still effective and healthy, but lost stamina. Three players, Davis, Campbell, and Smith (1994) had problems two seasons later, after another year of overuse. Only two of these players, Martin and Smith (1991) seemed to have no ill effects for multiple seasons afterwards.